Cheapest round?

A friend of mine had a home defense cd and the guy said your #1 gun in your safe zone should be a shotgun loaded with #9 or skeet load. These rounds will limit your penetration through walls into other rooms so that no one is injured in the path of fire. Also have in your safe zone a flashlight and some form of phone(cell). Mossberg sells a J.I.C which I have and its sweet!!!!